Linear motor cooling system

ABSTRACT

An apparatus includes an electric machine. The electric machine includes an internal housing, an armature coil disposed within the internal housing and separated from the internal housing by a gap, and a magnetic core associated with the armature coil. The apparatus also includes a fan configured to cause air to flow in the gap between the armature coil and the internal housing.

BACKGROUND

A linear motor is an electric motor that generates a linear force alongits length. The operation of such motors generates a significant amountof heat. Because many of the components of a linear motor, including, inparticular, the armature coils and associated magnetic cores, aresensitive to temperature, cooling systems are provided to avoid adeterioration in motor performance.

Referring to FIG. 1, one approach to cooling a linear motor 100 is toplace a heat sink 102 on either side of the motor. Heat generated duringthe operation of motor 100 is removed by conduction into heat sink 102.A fan bank 104 cools heat sink 102, thus dispersing the heat into thesurrounding atmosphere and cooling motor 100.

SUMMARY

In a general aspect, an apparatus includes an electric machine. Theelectric machine includes an internal housing, an armature coil disposedwithin the internal housing and separated from the internal housing by agap, and a magnetic core associated with the armature coil. Theapparatus also includes a fan configured to cause air to flow in the gapbetween the armature coil and the internal housing.

Embodiments may include one or more of the following.

The air flow in the gap causes cooling of at least one of the armaturecoil and the magnetic core.

The fan is configured to blow air directly across the armature coil

The apparatus further includes a plurality of fans. An arrangement ofthe plurality of fans is determined to maximize at least one of flowvelocity through the electric machine and heat transfer between the airand the armature coil.

The fan is configured to cause turbulent air flow in the gap.

A size of the gap is selected to cause turbulent air flow in the gap. Asize of the gap is selected to maximize heat transfer between the airand the armature coil.

The armature coil is a first armature coil and the magnetic core is afirst magnetic core; and further comprising: a second armature coiladjacent to the first armature coil, the first armature coil separatedfrom the second armature coil by a first coil gap; and a second magneticcore associated with the second armature coil. The fan is configured tocause air to flow in the first coil gap.

The apparatus further includes a third armature coil; and a fourtharmature coil adjacent to the third armature coil, the third armaturecoil separated from the fourth armature coil by a second coil gap. Thefan is configured to cause air to flow in the second coil gap.

The electric machine is an electromagnetic motor.

The apparatus further includes an inlet port is disposed on a first endof the electric machine, the fan disposed in the inlet port; and anexhaust port disposed on a second end of the electric machine oppositethe inlet port.

In another general aspect, a method includes providing an electricmachine. The electric machine includes an internal housing, an armaturecoil disposed within the internal housing and separated from theinternal housing by a gap, and a magnetic core associated with thearmature coil. The method further includes causing air to flow in thegap between the armature coil and the internal housing.

Embodiments may include one or more of the following.

Causing air to flow in the gap causes cooling of at least one of thearmature coil and the magnetic core. Causing air to flow in the gapcomprises blowing air directly across the armature coil. Causing air toflow in the gap causes turbulent air flow in the gap.

The method further includes determining a size of the gap in order tocause turbulent air flow in the gap. The method further includesdetermining a size of the gap in order to maximize heat transfer betweenthe air and the armature coil.

Among other advantages, the systems described herein have fewer partsand are less complex than conventional motor cooling systems and thuscan be implemented for lower cost. Gaps between armature coils withinthe motor allow for high cooling efficiency without compromising motorperformance, such as the output force of the motor. The ability to coolthe motor more efficiently allows the motor to be fabricated withconventional, lower cost lamination steel rather than higher gradesteel, thus further reducing the fabrication cost of the motor.

Other features and advantages of the invention are apparent from thefollowing description and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram of a prior art motor.

FIG. 2 is a diagram of a motor cooled by forced air cooling.

FIG. 3 is a diagram of internal components of the motor of FIG. 2.

FIG. 4A is a cut-away perspective view of the internal components ofFIG. 3.

FIG. 4B is a cut-away front view of the internal components of FIG. 3.

FIG. 4C is a cut-away side view of the internal components of FIG. 3.

DETAILED DESCRIPTION

Referring to FIGS. 2 and 3, a linear motor 200 outputs a linear forcealong its length (denoted as the x-axis). Motor 200 is formed of anexternal housing 201 which houses an internal body 203. Referring alsoto FIGS. 4A-4C, the internal body 203 includes four armature coils 202a, 202 b, 202 c, 202 d, each with an associated magnetic core 204 a, 204b, 204 c, 204 d, respectively. In operation, motor 200 generates asignificant amount of heat, primarily from current flowing through thearmature coils 202. The performance of the motor components, and inparticular the magnetic cores 204, decreases with increasing motortemperature.

A forced air, convection cooling system is employed to dissipate theheat generated by motor 200. In particular, a fan bank 206 is positionedat an inlet 208 on a front face 210 of the motor. Fan bank 206 includesone or more fans 212 that blow air directly into the interior of motor200. The air flow is generally along the length of armature coils 202(i.e., along the x-axis) and serves to cool the armature coils andassociated magnetic cores 204. Motor 200 is designed with a straightflow-through design in which flow restrictions, such as turns, bends, orlarge changes in cross-sectional area, are minimized. This unobstructeddesign allows air to flow through the motor at high velocity, whichprovides a high heat transfer coefficient between the air and the motorcomponents. The air exits the motor via an exhaust port 216 on a rearface 218 of the motor. In some embodiments, a filter 219 is positionedat inlet 208 prior to fan bank 206 and serves to filter the air that isdrawn into the motor, thus avoiding contamination of the motorcomponents.

In the interior of motor 200, open space is provided to facilitate airflow across armature coils 202 and magnetic cores 204. Gaps 222-228adjacent to the armature coils 202 allow a large fraction of the surfacearea of the armature coils to be exposed to the circulating air,facilitating heat transfer from the coils to the air. In particular, acentral gap 222 a separates armature coils 202 a and 202 b, and acentral gap 222 b separates armature coils 202 c and 202 d. Upper gaps224 a and 224 b separate armature coils 202 a and 202 c, respectively,from the top of an internal housing 220. Lower gaps 226 a and 226 bseparate armature coils 202 b and 202 d, respectively, from the bottomof housing 220. Side gaps 228 a, 228 b, 228 c, and 228 d separatearmature coils 202 a, 202 b, 202 c, and 202 d, respectively, from acentral support core 229 of the housing 220.

High velocity air flow enhances the heat transfer coefficient betweenthe armature coils 202 and the circulating air. The volume of spaceavailable for air flow (i.e., the size and geometry of the gaps) affectsthe system impedance to air flow and thus influences the velocity of theair passing through the motor. The air flow velocity is also dependentupon the performance of fan bank 206, as well as on environmentalfactors such as temperature and air density.

The heat transfer coefficient is maximized for turbulent air flowthrough the motor. Turbulent air flow can be achieved by causing air ofsufficiently high velocity to flow in gaps 222-228, which is effected byoptimizing the fan arrangement and performance and the gap geometry.However, cost and manufacturing considerations dictate that a motor ofsmaller volume and with a minimum number of fans is desirable. Thus, inpractice, the gap geometry and fan arrangement are determined via aniterative process which aims to both maximize the heat transfercoefficient and minimize manufacturing cost. The amount of heatdissipated by the armature coils 202 is generally known. Factors such asthe maximum allowable operating temperature of the armature coils 202and magnets 204, the properties of the fluid (i.e., the circulating air)at the operating temperature, the airflow impedance of the motor, thefan performance curves, and the fan arrangement and cost are used asparameters in a model of the motor and cooling system. The design of themotor is determined to optimize the performance of the cooling system.

As an example, given the heat dissipation by the armature coils 202, themaximum ambient temperature, and an understanding of the temperaturelimitations of the coils and magnets, the heat transfer coefficient thatis sufficient to limit the temperatures of sensitive motor componentscan be calculated. Because the heat transfer coefficient is a functionof the properties of the fluid, the flow velocity, and the flowgeometry, it is possible to iterate a motor design in order to optimizethe design for performance and cost. For instance, reducing the gapbetween the coils increases the impedance of the motor to air flow; tocompensate for the increased impedance, the fan performance is increasedto produce sufficient velocity to achieve the desired heat transfercoefficient. A larger gap between the coils will lower the air flowimpedance but generally necessitates higher air flow rates to obtain thedesired heat transfer coefficient. Thus, in general, an iterativeprocess using motor impedance (i.e., geometry and/or gap size), fanperformance, and cost as variables is employed to optimize the design ofthe motor.

As an example, a motor designed based on such an iterative processproduces 7.5 kN of force output and dissipates about 1.8 kW of heatthrough its four armature coils, or 450 Watts per coil. The gaps aboveand between the coils are 10 mm. The motor has external dimensions of44.5 cm×27.2 cm×43.7 cm and weighs approximately 95 kg.

The arrangement of gaps 222-228 is also subject to maintaining suitablemagnetic performance of the motor components. In a conventional motorwith no gaps between the armature coils, the magnet transition line(i.e., the N-to-S magnetic orientation change) is aligned with thecenters of the pole faces. In a motor with gaps between the coils, thisalignment of the magnet transition line is maintained. Furthermore, theinclusion of the gaps between the armature coils increases the distancebetween the poles but continues to keep the magnetic transition distancealigned with the pole face centers.

It is to be understood that the foregoing description is intended toillustrate and not to limit the scope of the invention, which is definedby the scope of the appended claims. Other embodiments are within thescope of the following claims.

1-20. (canceled)
 21. An apparatus comprising: a linear motor disposed togenerate a linear force, the linear motor including: a first armaturecoil associated with a first magnetic core and disposed within aninternal housing; a second armature coil associated with a secondmagnetic core and disposed within the internal housing; and a centralsupport core extending from a top of the internal housing to a bottom ofthe internal housing and disposed between the first armature coil andthe second armature coil; wherein the central support core defines afirst side gap separating the first armature coil from the centralsupport core and a second side gap separating the second armature coilfrom the central support core.
 22. The apparatus of claim 21, wherein afirst portion of the top of the internal housing and the first armaturecoil define a first upper gap allowing air to flow along a length of thefirst armature coil, and a second portion of the top of the internalhousing and the second armature coil define a second upper gap allowingair to flow along a length of the second armature coil.
 23. Theapparatus of claim 21, further comprising: a third armature coilassociated with a third magnetic core and disposed within the internalhousing adjacent to the first armature coil; and a fourth armature coilassociated with a fourth magnetic core and disposed within the internalhousing adjacent to the second armature coil; wherein the centralsupport core is disposed between the third armature coil and the fourtharmature coil.
 24. The apparatus of claim 23, wherein a first portion ofthe bottom of the internal housing and the third armature coil define afirst lower gap allowing air to flow along a length of the thirdarmature coil, and a second portion of the bottom of the internalhousing and the fourth armature coil define a second lower gap allowingair to flow along a length of the fourth armature coil.
 25. Theapparatus of claim 23, wherein a portion of the first armature coil anda portion of the third armature coil define a first central gap betweenthe first armature coil and the third armature coil, and wherein aportion of the second armature coil and a portion of the fourth armaturecoil define a second central gap between the second armature coil andthe fourth armature coil.
 26. The apparatus of claim 23, wherein thecentral support core further defines a third side gap separating thethird armature coil from the central support core and a fourth side gapseparating the fourth armature coil from the central support core. 27.The apparatus of claim 26, wherein the third side gap is configured toallow air to flow in contact with the third magnetic core and the fourthside gap is configured to allow air to flow in contact with the fourthmagnetic core.
 28. The apparatus of claim 26, wherein the third side gapand the fourth side gap are configured to allow air to flow in adirection substantially parallel to the linear force of the linearmotor.
 29. The apparatus of claim 21, wherein the first side gap isconfigured to allow air to flow in contact with the first magnetic coreand the second side gap is configured to allow air to flow in contactwith the second magnetic core.
 30. The apparatus of claim 21, whereinthe first side gap and the second side gap are configured to allow airto flow in a direction substantially parallel to the linear force of thelinear motor.
 31. A method of cooling armature coils of a linear motor,the method comprising: providing a linear motor disposed to generate alinear force, the linear motor comprising: a first armature coilassociated with a first magnetic core and disposed within an internalhousing; a second armature coil associated with a second magnetic coreand disposed within the internal housing; and a central support coreextending from a top of the internal housing to a bottom of the internalhousing and disposed between the first armature coil and the secondarmature coil; flowing air in contact with the first magnetic corethrough a first side gap separating the first armature coil from thecentral support core; and flowing air in contact with the secondmagnetic core through a second side gap separating the second armaturecoil from the central support core.
 32. The method of claim 31, whereinflowing air through the first side gap and flowing air through thesecond side gap includes operating a fan to direct a turbulent air flowthrough the first side gap and the second side gap in a directionsubstantially parallel to the linear force of the linear motor.
 33. Themethod of claim 31, further comprising: flowing air along a length ofthe first armature coil through a first upper gap defined by a firstportion of the top of the internal housing and the first armature coil;and flowing air along a length of the second armature coil through asecond upper gap defined by a second portion of the top of the internalhousing and the second armature coil.
 34. The method of claim 31,wherein the linear motor further comprises: a third armature coilassociated with a third magnetic core and disposed within the internalhousing adjacent to the first armature coil; and a fourth armature coilassociated with a fourth magnetic core and disposed within the internalhousing adjacent to the second armature coil, wherein the centralsupport core is disposed between the third armature coil and the fourtharmature coil; wherein the method further comprises: flowing air incontact with the third magnetic core through a third side gap defined bythe central support core and the third armature coil; and flowing air incontact with the fourth magnetic core through a fourth side gap definedby the central support core and the fourth armature coil.
 35. The methodof claim 34, further comprising: flowing air along a length of the thirdarmature coil through a first lower gap defined by a first portion ofthe bottom of the internal housing and the third armature coil; andflowing air along a length of the fourth armature coil through a secondlower gap defined by a second portion of the bottom of the internalhousing and the fourth armature coil.
 36. The method of claim 34,further comprising: flowing air through a first central gap between thefirst armature coil and the third armature coil; and flowing air througha second central gap between the second armature coil and the fourtharmature coil.